In a railway car, primary and secondary suspension systems are generally employed. The primary suspension system refers to the suspension between the journal bearing assemblies and the truck frame. The journal bearing assemblies carry wheel-axle units and acceleration forces generated by the wheels riding over the rails. These forces are transmitted through the primary suspension system to the side frames of the truck. The secondary system refers to the suspension system between a bolster on the car body and the truck and may include air or mechanical springs, for example. The present invention is directed to primary suspension systems.
There are presently in use railway cars in which the primary suspension system includes rubber so-called shock rings fitted between a journal bearing assembly and side frames of the truck. The rubber rings used are compressed and clamped between the journal assemblies and side frame.
Very often such rings result in high vertical and longitudinal stiffness. Relatively high vertical stiffness in the primary suspension systems results in very little attenuation of the wheel accelerations to the truck frame. The relatively high longitudinal stiffness tends to maintain the axle position or wheel base within the truck frame limiting the extent to which the axles can steer while curving.
While the use of rubber rings in primary suspension systems has proven satisfactory in many situations, it has the disadvantage of compression set and aging. The use of rubber in the suspension system generally requires replacements of the rubber elements involved which is undesirable from a long term maintenance point of view.
In addition to limiting the acceleration levels experienced in a truck, it is also desirable for a primary suspension system to have sufficient longitudinal compliance to allow the axles on the truck to self-steer and align themselves properly with the rails, a feature not found in so-called non-spring or rigid systems.